Variability of Selected Traits of Ips Typographus (L.) (Col.: Scolytinae) Populations In Beskid Żwiecki (Western Carpathians, Poland) Region Affected By Bark Beetle Outbreak

Abstract

In 2010-2012, investigations on Ips typographus populations were carried out in Norway spruce stands recently affected by bark beetle outbreak in the Beskid Żywiecki Mts. in Poland. The aim of the study was to test the usefulness of several traits describing I. typographus populations for evaluation of their actual outbreak tendency. Infestation density, sex ratio, gallery length, progeny number and beetle length were used as the traits. Trait variability was analyzed in relation to infested tree mortality in the current year of observation and outbreak tendency defined by the comparison of data on tree mortality in the current year and that in the year before. The highest infestation density was found in the stands representing the highest tree mortality in the current year and in those characterized by decreasing outbreak tendency. The gallery system with 2 maternal galleries dominated. The sex ratio of attacking beetles inclined towards females (63.8%) and remained stable during 3 years of observations; the highest percentage of females was found in locations being in stabilization/latency outbreak phase. The length of maternal galleries was somewhat negatively affected by infestation density and positively correlated with the number of progeny in the gallery. The average beetle length was 4.800 mm (± 0.293), ranging between 3.718 and 5.817 mm and being the highest in the uppermost class of tree mortality recorded in the current year of observation. The shortest beetles were collected in the stands with increasing outbreak tendency, and slightly longer - in the stands with outbreak stable and decreasing tendencies. None of the traits tested can be selected as a direct indicator for prediction of outbreak tendency in I. typographus populations. Possible reasons of variability in the analyzed traits are discussed. The traits indicate that I. typographus in the study area represent very high reproductive potential, thus the risk of repeated outbreak is very high

Reproduction abilities of Ips typographus (L.) (Coleoptera: Curculionidae, Scolytinae) in the stands damaged by the wind in 2013 in the Kościeliska Valley (Tatra National Park)

“…(observed: 16.22 ± 6.95; expected 1: 16.24 ± 3.25) are close to those (expected 3: 17.29 ± 4.35) estimated using the equation from Beskidy Mts. (Grodzki et al 2014) and far lower than the values (expected 2: 27.97 ± 6.84) resulting from the equation proposed by Anderbrant (1990) (Fig. 5).…”

“…When applying the simple regression model describing the relationship between the gallery length and number of progeny (see Fig. 3), as well as the other models based on the length of the maternal gallery proposed by Anderbrant (1990) and Grodzki et al (2014), both observed and expected average values from Kościeliska Valley were lower than the average number calculated using those models (Fig. 5).…”

“…-6.75 cm (Grodzki et al 2014) -as well as previously from Šumava Mts. in the Czech Republic -7.8 cm (Matoušek et al 2012) -and from Bieszczady Mts.…”

“…5. Number of progeny per female calculated using three different models: expected 1, based on the actual correlation; expected 2, based on the regression model proposed by Anderbrant (1990); expected 3, based on the regression model proposed by Grodzki et al (2014) The estimation of expected number of progeny based on the maternal gallery length and resulting regression equation is not exact (Wilcoxon paired test -observed vs. expected 1: N = 1,891, T = 820,015.0, Z = 3.134, p = 0.0017); however, both average values from the Tatra Mts. (observed: 16.22 ± 6.95; expected 1: 16.24 ± 3.25) are close to those (expected 3: 17.29 ± 4.35) estimated using the equation from Beskidy Mts.…”

“…-23.1 (Lukášová et al 2012) -and Beskidy Mts. -21.3 per female (Grodzki et al 2014). When applying the simple regression model describing the relationship between the gallery length and number of progeny (see Fig.…”